Steve Underwood wrote:
In my experience, compilers typically do what mspgcc currently does now. If you try to access an unaligned integer in a structure on a processor which doesn't like it, they don't warn you, but the code crashes.
Really? I'm not sure I'd be impressed with that. I'm just trying to recall what happened with PDP-11 and things in the old days.
That's what the Alpha and MIPs compilers I have used did. Later versions of Alpha allowed misalignment with a speed penalty, like the x86.
Yeah, but that's the hardware, not the code.
I'm not sure if MIPs ever changed. Now, the question is, what do people really expect on a thing like the MSP430.If you try something like struct { int x; char y; } xxx[10];and loop through the array accessing x, all is well. If you pack the structure it fails with mspgcc. The only real difference in the generated code is the loop steps 3 bytes at a time instead of 4. Now, if you try this with the IAR compiler for the MSP430, things still work with the packed structure. However, to achieve that complex code is produced when the structure is packed, and simple code is produced when it is not. Is this something people would like to see in mspgcc?
It's an interesting dilemma. My opinion is that it should do what the IAR compiler does, but generate a warning. Alternatively, fail to compile with an error message explaining the issue.
The big thing about compiling for compact embedded environments where the MSP430 is often found is that there just isn't the code space to allow code bloat due to possible user mistakes like packing inappropriate structs. A warning would be the least I'd expect.
Steve.
